Alterations in the respiratory mechanics of unanesthetized guinea pigs will be used as a biological assay for irritant response. It is proposed to examine the dose-response aspects of the increased sensitivity of the lung to irritent materials produced by exposure to ozone. Guinea pigs will be exposed for 2 hr to 0.2, 0.4 and 0.8 ppm ozone. At intervals ranging from 90 min to 24 hr (longer if results warrant) they will be given an injection of histamine or acetyl choline which has been found to produce a standard alteration in pulmonary mechanics. It will be determined whether altered responses to these agents are best related to concentration or to total dose of ozone (C x T). The effect of prior ozone exposure on the irritant response to materials such as ammonium sulfate, zinc ammonium sulfate, and sulfur dioxide alone and in the presence of particles will also be determined. A similar series of studies is proposed for nitrogen dioxide. Studies are also proposed on the effect of carbon particles on the response to sulfur dioxide under conditions of both low (R>H> 50%) and high (R>H> 80%) humidity. If time permits, the interaction of carbon particles with nitrogen oxides will also be examined. Studies are proposed on the combined effect of sulfur dioxide and formaldehyde and on the chemical complex formed by these two irritants.